In thermal dye transfer printing, an image is formed on a receptor sheet by selectively transferring a dye to a receptor sheet from a dye donor sheet placed in momentary contact with the receptor sheet. Material to be transferred from the dye donor sheet is directed by a thermal printhead, which consists of small electrically heated elements (print heads). These elements transfer image-forming material from the dye donor sheet to areas of the dye receptor sheet in an image-wise manner. Thermal dye transfer systems have advantages over other thermal transfer systems, such as chemical reaction systems, and thermal mass transfer systems. In general thermal dye transfer systems offer greater control of gray scale than these other systems, but they have problems as well. One problem is release of the dye donor and receptor layers during printing. This has been addressed often by the addition of dye-permeable release coatings applied to the surface of the dye receptor layer. Additionally, materials are required for use in the receptor layer having suitable dye permeability, mordanting properties, adhesion to the substrate, and long term light and thermal stability.
Recent advances in thermal dye transfer imaging systems describe thermal dye transfer receptor layers which can be coated out of solution and used on various surfaces to provide a high quality dye receiving layer. Such materials are described in U.S. Pat. Nos. 4,914,078 and 4,968, 658. These layers are coated out of solution from presently acceptable solvents such as methyl ethyl ketone.
Polyvinyl chloride derivatives and copolymers have been heavily used in thermal dye transfer receptor sheets as receptor layers, because of their properties in these areas. For example, U.S. Pat. No. 4,853,365 discloses that chlorinated polyvinyl chloride, used as a dye receptor, has good dye solubility and high dye receptivity. Similarly, vinyl chloride/vinyl acetate copolymers have also been used as receptor layers in thermal dye transfer receptor sheets as described in Japanese published application nos. 29,391 (1990) and 39,995 (1990). Japanese published application no. 160,681 (1989) discloses dye acceptance layers comprising polyvinyl chloride-polyvinyl alcohol copolymers, and Japanese published application nos. 43,092 (1990), 95,891 (1990) and 108,591 (1990) discloses dye image receiving layers comprising a hydroxy modified polyvinyl chloride resin and an isocyanate compound. U.S. Pat. No. 4,897,377 discloses a thermal transfer printing receiver sheet comprising a supporting substrate coated on at least one surface with an amorphous polyester resin. Published European patent application 133,012 (1985) discloses a heat transferable sheet having a substrate and an image-receiving layer thereon comprising a resin having an ester, urethane, amide, urea, or highly polar linkage, and a dye-releasing agent, such as a silicone oil, being present either in the image-receiving layer or as a release layer on at least part of the image receiving layer. Published European patent application 133,011 (1985) discloses a heat transferable sheet based on imaging layer materials comprising first and second regions respectively comprising (a) a synthetic resin having a glass transition temperature of from -100.degree. to 20.degree. C., and having a polar group, and (b) a synthetic resin having a glass transition temperature of 40.degree. C. or above.
U.S. Pat. No. 4,968,658 teaches the use of a thermal transfer receptor surface with a receiver coating comprising a dye-receptive material, a dye-permeable release agent, and an alkoxylated Bisphenol A unsaturated polyester. Fumaric acid may also be used in the layer.